The field of microfluidics has gained substantial attention as a potential answer to many of the problems inherent in conventional chemical, biochemical and biological analysis, synthesis and experimentation. In particular, by miniaturizing substantial portions of laboratory experimentation previously performed at a lab bench, one can gain substantial advantages in terms of speed, cost, automatability, and reproducibility of that experimentation. This substantial level of attention has led to a variety of developments aimed at accomplishing that miniaturization, e.g., in fluid and material handling, detection and the like.
U.S. Pat. No. 5,271,724 to van Lintel, for example reports a microscale pump/valve assembly fabricated from silicon using manufacturing techniques typically employed in the electronics and semiconductor industries. The microscale pump includes a miniature flexible diaphragm as one wall of a pump chamber, and having a piezoelectric element mounted upon its exterior surface.
Similarly, U.S. Pat. No. 5,375,979 to Trah, reports a mechanical micropump/valve assembly that is fabricated from three substrate layers. The pump/valve assembly consists of a top cover layer disposed over a middle layer having a cavity fabricated therein, to define the pumping chamber. The bottom layer is mated with the middle layer and together, these substrates define each of two, one way flap valves. The inlet valve consists of a thin flap of the middle substrate layer that is disposed over an inlet port in the bottom substrate layer, and seated against the bottom layer, such that the flap valve will only open inward toward the pump chamber. A similar but opposite construction is used on the outlet valve, where the thin flap is fabricated from the bottom layer, is seated over the outlet port and against the middle layer such that the valve only opens away from the pump chamber. The pump and valves cooperate to ensure that fluid moves in only one direction.
Published PCT Application No. 97/02357 reports an integrated microfluidic device incorporating a microfluidic flow system in combination with an oligonucleotide array. The microfluidic system moves fluid by application of external pressures, e.g., via a pneumatic manifold, or through the use of diaphragm pumps and valves.
While these microfabricated pumps and valves provide one means of transporting fluids within microfabricated substrates, their fabrication methods and materials can be somewhat complex, resulting in excessive volume requirements, as well as resulting in an expensive manufacturing process.
Published PCT Application No. 96/04547 to Ramsey, describes an elegant method of transporting and directing fluids through an interconnected channel structure using controlled electrokinetic forces at the intersections of the channels, to control the flow of material at those intersections. These material transport systems employ electrodes disposed in contact with the various channel structures to apply the controlled electrokinetic forces. These methods have been adapted for a variety of applications, e.g., performing standard assays, screening of test compounds, and separation/sequencing of nucleic acids, and the like. See, e.g., commonly assigned U.S. patent application Ser. No. 08/761,575, filed Dec. 6, 1996, now U.S. Pat. No. 6,046,056, U.S. Patent Application Ser. No. 60/086,240, filed Apr. 4, 1997 U.S. Pat. No. 5,976,336 and U.S. patent application Ser. No. 08/845,754 now U.S. Pat. No. 5,976,336, filed Apr. 25, 1997, all of which are incorporated herein by reference in its entirety for all purposes. These "solid state" material transport systems combine a high degree of controllability with an ease of manufacturing.
Despite the numerous advantages of using controlled electrokinetic material transport in microfluidic systems, in some cases it is desirable to combine the ease of control and fabrication attendant to such systems with the benefits of pressure-based fluid transport systems. The present invention meets these and other needs.